replaced broken power law model code with C++

Rationalized the broken power law model code. Rewritten in C++ and calls powerLaw to evaluate individual sections of the model.

cflux model

One thing to note about the cflux model which is not clear in the documentation is that the model component(s) to which cflux is applied must integrate to a non-zero flux. For instance, cflux*pow where the pow norm is zero will generate NaNs from a divide-by-zero.

obscure extractor bug

Under some circumstances ROTANG elements in the output region extension could have junk values but only for region types where the rotation angle is irrelevant. This is fixed in extractor v5.14.

updated xselect XMM script

Updated the script run by save spectrum in the XMM case since I had assumed that CCDNR was the first DS keyword which appears not to always be the case.